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Museum Pieces: Mercury-Redstone 4, "Liberty Bell 7" [1]

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Date: 2023-09-05

The Mercury-Redstone 4 mission was textbook perfect—until it was almost over.

"Museum Pieces" is a diary series that explores the history behind some of the most interesting museum exhibits and historical places.

Liberty Bell 7, on display at the Cosmosphere Museum in Hutchinson KS

After the successful suborbital flight by Alan Shepard and Freedom 7 in May 1961, NASA scheduled a second suborbital mission for July, designated Mercury-Redstone 4 and piloted by Virgil "Gus" Grissom. Grissom was an Air Force test pilot with over 100 combat missions in Korea before being selected as an astronaut.

Grissom's mission would be a virtual carbon-copy of Shepard's flight, but would have the additional aims of flight-testing some changes that had been made in the Mercury design too late to be included on Freedom 7. Shepard's ship had only been provided with two tiny portholes, giving only limited visibility. The astronauts objected to this strongly, and NASA agreed to modify the newer spaceships with a much larger glass window so the pilot could see outside. Some technical changes were also made to the pressurization, the attitude controls, and the heat shield release systems. In addition, the recovery crew was set to deploy a new inflatable flotation collar which would fit around the bottom of the capsule as it floated in the water, to stabilize it.

Most significantly, however, the hatch had been modified. In the original design, the hatch had been sealed with a heavy latch which had to be laboriously cranked by hand, making it impossible in an emergency to open the capsule quickly and extract the pilot. This hatch assembly also weighed a whopping 69 pounds, and this needed to be reduced drastically for orbital missions. So the original Mercury hatch was modified to use 70 titanium bolts to secure it to the spaceship. The new version weighed only 23 pounds, but it was still a painfully slow process to unscrew the 70 separate bolts to open the hatch in an emergency. So the hatch was further modified by lining the hatch seal with an explosive cord which would, if detonated, sever all the bolts and pop the hatch off in less than a second. The explosive charge could be detonated from the inside by the astronaut using a mechanical plunger switch, or from the outside by the recovery crew using a covered lanyard switch. Similar explosive-bolts systems had already long been in use for high-performance aircraft.

Grissom had named his ship "Liberty Bell 7", and this name, along with a symbolic crack, was duly painted onto the side of the spacecraft. The flight was intended to last only 15 minutes, with the Redstone booster rocket taking the spaceship from the launch pad at Cape Canaveral to about 100 nautical miles up before allowing the capsule to fall back to Earth in a parabolic arc, under the force of gravity. Grissom would be weightless for about 5 minutes.

Originally scheduled for July 18, the mission was pushed back four hours by a weather delay and then was finally rescheduled to July 21. On that day, after several short holds (one due to bad weather, and another caused by a hatch bolt that had been cross-threaded during closing), Liberty Bell 7 lifted off at 7:20am.

After about five minutes, the Redstone rocket's engines shut down and the explosive bolts which held the Mercury capsule to the missile detonated, separating them. While the Redstone fell back to Earth to burn up in the atmosphere, control thrusters automatically turned Liberty Bell 7 around until her heat shield was facing forward in re-entry configuration.

For the next five minutes, Grissom was weightless in space (though he was strapped to his seat so tightly that he was barely able to feel it). His tasks during this time included several test-firings of the maneuvering thrusters that were used to change the spacecraft's orientation as it flew along.

Although the spacecraft did not have enough energy to enter orbit and would have fallen back to Earth by itself under gravity, Grissom, as a test, fired the retrorocket package that would, on the upcoming orbital missions, slow the Mercury down enough for re-entry. After falling through the atmosphere for a short time, the ship reached a height of 22,000 feet, which caused the first set of parachutes to automatically deploy. A short time later, the heat shield was released and fell, pulling the landing bag after it. This air-filled bag was intended to act as a cushion when Liberty Bell 7 hit the water.

The recovery ship, the aircraft carrier Randolph, was already in position, and search planes caught sight of Liberty Bell as she was floating towards the sea, her main parachutes deployed. Touchdown happened at 15 minutes and 37 seconds after launch. Upon entering the water, the ship released a packet of fluorescent green dye, which served as a visual beacon for the search aircraft to help them spot the tiny capsule as it bobbed in the waves. The recovery helicopters were only two miles away.

Until now, Mercury-Redstone 4 had been a picture-perfect mission. But then something went wrong.

The recovery helicopter had already moved in and attached a cable to the Mercury craft, which they would use to carry the spaceship back to the carrier. While waiting for the crew to reach him, Grissom, still sitting in his molded flight seat, began going through the post-flight checklist and writing down various instrument readings. Suddenly, without warning, the explosive bolts on the hatch went off, the covering went flying away into the air, and sea water began pouring in through the now-open entrance.

Grissom was forced to make a rapid exit into the open sea, but now he was in even more trouble. He had not yet closed the valve in his suit that had attached to the Mercury's oxygen hose, and now water began pouring inside his spacesuit through the open connector. As he began to sink, he waved frantically to the recovery helicopter--but they assumed he was telling them that he was okay and signaling them to save the spacecraft. It wasn't until the pilot of the second helicopter realized that Grissom was barely keeping afloat that he moved in and dropped a rescue line. Grissom, half-drowned, was pulled up to safety.

The first helicopter was now trying to lift the Liberty Bell capsule, but over a ton of water had now flooded inside, and the weight was far beyond the Sikorsky's lifting capacity. As the chopper strained to lift the capsule, its own landing gear wheels dipped in the water. When the red warning lights began to flash on the pilot's instrument panel indicating metal chips in the engine oil, he made the decision to disconnect the lifting cable. Liberty Bell 7 promptly sank out of sight and settled on the bottom of the Atlantic Ocean, three miles below.

Grissom was flown to the Randolph where, still dripping wet, he received a congratulatory telephone call from President John Kennedy.

NASA immediately began an investigation to determine what had happened to the hatch. Initial suspicion of course first fell on Grissom, with some people theorizing that he had either intentionally or accidentally hit the switch and blown the hatch too soon. Although this theory still turns up from various researchers (and was featured in a famous book and movie about the Mercury project), NASA soon rejected it. There was simply no plausible way to hit the switch from the pilot's couch. (Later, other astronauts discovered that the switch had a very strong spring, and when they hit the button during their missions, they received a small crescent-shaped bruise on the palm of their hand--which Grissom did not have.) Grissom eventually reached the conclusion that the external lanyard had come loose and accidentally triggered the switch. NASA later discovered that the explosive hatches sometimes had a vacuum build up inside the firing pin channels, which could lead to a spontaneous explosion. Today, the most popular theory seems to be that the recovery helicopter had built up a static electrical charge during its flight which was transferred to the spaceship during hookup, and that this was enough to prematurely set off the explosives charge inside the hatch.

Grissom went on to command the first of the manned Gemini missions, and, with grim humor, named his Gemini 3 spaceship "The Unsinkable Molly Brown" after a popular Broadway musical. NASA was unamused, and quickly banned future Gemini commanders from naming their ships.

But Liberty Bell 7's story wasn't over yet.

In 1978, the new Cosmosphere space museum in Hutchinson KS, an hour away from Wichita, was looking for a space-flown Mercury spaceship to add to its display collection. But all of the Mercury capsules, including all of the unmanned test flights, had already been parceled out by NASA to various museums. The only one that was not on exhibit was Liberty Bell 7, and that was still at the bottom of the Atlantic.

Undaunted, the museum decided to launch an effort to find, raise, and restore the lost spaceship. After much research, they narrowed down a search area surrounding the known position of the recovery ships. But at this time there was no technology available that could carry out the search, and when submersible submarines and camera arrays capable of surveying at that depth finally appeared in the 1980s, there still remained the problem of funding such an effort.

Then, in the early 1990s, the TV cable network The Discovery Channel stepped in and agreed to fund an expedition in exchange for the broadcast rights. They formed a joint company called Oceaneering International Inc and organized an expedition. NASA in turn agreed to sign away ownership of the spaceship and abandon all rights to it.

The process was similar to that used to find the wreck of the Titanic. A sonar array was towed back and forth over the search area, and any interesting targets on the seafloor were noted. Later, these would be investigated, one at a time, by deep-water camera systems which would identify them. But unlike the immense Titanic, the Liberty Bell 7 was barely bigger than a phone booth, and finding her was not an easy task. The first two expeditions, in 1992 and 1993, found nothing but rocks and bits of random junk.

A new expedition was undertaken in April 1999. After covering a 24-square mile area with the side-scan sonar, the team had found 88 possible targets, and narrowed this down to 18 which they would investigate using an array of cameras mounted on an ROV. At their very first target, the ROV hit paydirt. There, sitting on the seafloor, was Liberty Bell 7, still in remarkably good condition after almost four decades underwater.

But then bad luck struck: the ROV's control cable snapped, and the million-dollar rig joined the Mercury spacecraft on the ocean bed. It took the team three months to form another expedition and return to the site, and they were able to recover both the lost ROV and the spaceship. On July 21, 1999, exactly 38 years after Grissom's flight, Liberty Bell 7 was raised onto the deck of the recovery ship.

The Cosmosphere team already had extensive experience with restoring spacecraft for other museums, including the Smithsonian. So the restoration of Grissom's lost spaceship went smoothly. After a six-month process to reverse the corrosion caused by salt water, the Liberty Bell 7 was finally restored and, after a six-year tour around the country, went on permanent display at the Cosmosphere museum in 2020.

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